The present invention relates to an electro-optical monitoring system. The invention is particularly useful in systems for monitoring vehicles, e.g. in anti-collision systems, and in vehicle-identification systems, and is therefore described below with respect to these applications.
One important application of vehicle monitoring systems is for reducing the danger of collisions. Many of the anti-collision systems which have been devised are based on the echo-type detectors for continuously measuring the distance between two vehicles, and the rate-of-change of such distance, in order to produce a visual and/or audible signal or alarm should the distance between the two vehicles be less than a safe stopping distance predetermined for the respective velocity and rate-of-change of such distance. However, such known anti-collision systems have not proved satisfactory as evidenced by the fact that they have not been widely adopted. Moreover, such systems cannot monitor other road conditions, such as road signs, traffic lights and the like, to provide other information which may also be useful to the monitoring vehicle for increasing the safety in the operation of the monitoring vehicle.
Another important application of vehicle monitoring systems is for identifying vehicles, for example when the vehicles enter toll roads, toll bridges or the like, not only for statistical purposes, but also for determining toll charges. Previous proposals for monitoring vehicles for this purpose, such as reading the vehicle license plate number, have been relatively slow and/or unreliable.